Various downhole components use control lines for operation. For example, subsurface safety valves, such as tubing retrievable safety valves, deploy on production tubing in a producing well. Actuated by hydraulics via a control line, the safety valve can selectively seal fluid flow through the production tubing if a failure or hazardous condition occurs at the well surface. In this way, the safety valve can minimize the loss of reservoir resources or production equipment resulting from catastrophic subsurface events.
One type of safety valve is a deep-set safety valve that uses two control lines for operation. One active control line controls the opening and closing of the safety valve's closure, while the other control line is used for “balance.” Due to the deep setting of the valve, this balance control line negates the effect of hydrostatic pressure from the active control line.
In FIG. 1, for example, production tubing 20 has a deep-set safety valve 40 for controlling the flow of fluid in the production tubing 20. In this example, the wellbore 10 has been lined with casing 12 with perforations 16 for communicating with the surrounding formation 18. The production tubing 20 with the safety valve 40 deploys in the wellbore 10 to a predetermined depth. Produced fluid flows into the production tubing 20 through a sliding sleeve or other type of device. Traveling up the tubing 20, the produced fluid flows up through the safety valve 40, through a surface valve 25, and into a flow line 22.
As is known, the flow of the produced fluid can be stopped at any time during production by switching the safety valve 40 from an open condition to a closed condition. To that end, a hydraulic system having a pump 30 draws hydraulic fluid from a reservoir 35 and communicates with the safety valve 40 via a first control line 32A. When actuated, the pump 30 exerts a control pressure PC through the control line 32A to the safety valve 40.
Due to vertical height of the control line 32A, a hydrostatic pressure PH also exerts on the valve 40 through the control line 32A. For this reason, a balance line 32B also extends to the valve 40 and provides fluid communication between the reservoir 35 or pressure from pump 31 and the valve 40. Because the balance line 32B has the same column of fluid as the control line 32A, the outlet of the balance line 32B connected to the valve 40 has the same hydrostatic pressure PH as the control line 32A.
As with the deep-set safety valve, there may be other reasons to run multiple control lines downhole to components. Unfortunately, the control lines have to pass uphole to a wellhead. Communicating with multiple control lines through a wellhead can present a number of challenges due to limited space, installation complexity, and sealing issues. The difficulties are exacerbated when subsea wellhead equipment is used. In general, subsea wellhead equipment has restrictions on how many penetrations can be made through it for the use of control lines, fiber optics, etc.
Typically, intelligent well completions, deep-set safety valves, and other well system require two or more control lines penetrating the wellhead and running downhole. However, current control line systems have limitations due to the restrictions on the number of wellhead penetrations that can be made as well as issues pertaining to when one of the control lines ruptures.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.